Batch child objects using transactions

[cbaker6]

Currently, when child objects are present they are saved to the server individually which requires more network calls and overhead. This was done on purpose because child objects are discovered at the ParseEncoder level and returned as an opaque Encodable object. This caused issues with using batch... This PR addresses the problem by making those opaque objects AnyCodable, allowing batch to do its thing. In addition, each batch of child objects are always sent as a transaction.

• Enable batches child objects
• Send child objects as transactions by default
• Adjust test cases
• Bug fix - linking an anonymous user was using an old sessionToken, resulting in an invalid session token error after becoming a real user
• Add entry to changelog

This PR is non-breaking as all of the changes are under-the-hood

[codecov]

Codecov Report

Merging #94 (e903025) into main (82cbecd) will increase coverage by 0.12%.
The diff coverage is 77.97%.

❗ Current head e903025 differs from pull request most recent head dc76154. Consider uploading reports for the commit dc76154 to get more accurate results

@@            Coverage Diff             @@
##             main      #94      +/-   ##
==========================================
+ Coverage   78.95%   79.08%   +0.12%     
==========================================
  Files          63       63              
  Lines        5114     5179      +65     
==========================================
+ Hits         4038     4096      +58     
- Misses       1076     1083       +7     

Impacted Files	Coverage Δ
Sources/ParseSwift/API/BatchUtils.swift	100.00% <ø> (ø)
Sources/ParseSwift/API/Responses.swift	88.57% <ø> (+21.18%)	⬆️
Sources/ParseSwift/Coding/AnyCodable.swift	53.70% <ø> (-3.20%)	⬇️
...Authentication/Protocols/ParseAuthentication.swift	70.09% <50.00%> (-3.65%)	⬇️
Sources/ParseSwift/Objects/ParseUser.swift	79.16% <70.83%> (+2.70%)	⬆️
Sources/ParseSwift/API/API+Commands.swift	78.32% <93.47%> (-4.41%)	⬇️
Sources/ParseSwift/Coding/AnyEncodable.swift	30.49% <100.00%> (+0.09%)	⬆️
Sources/ParseSwift/Coding/ParseCoding.swift	89.13% <100.00%> (ø)
Sources/ParseSwift/Objects/ParseObject.swift	77.22% <100.00%> (-0.23%)	⬇️
... and 1 more

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